Polyphosphides are negatively charged clusters of phosphorus atoms that exhibit multifarious structural motifs. The majority of polyphosphides had been obtained by direct solid-state reactions between metals and red phosphorus red, (Pred) or by iodine-assisted chemical vapor transport (von Schnering & Hönle, Chemistry and structural chemistry of phosphides and polyphosphides. 48. Bridging chasms with polyphosphides. Chem. Rev., 1988 January; 88 (1): 243-273; Pöttgen, W. Hönle, H. G. von Schnering in Encyclopedia of Inorganic Chemistry, Vol. 8, 2nd ed. (Ed.: R. B. King), Wiley, Chichester, 2005, p. 4268). Only a handful of uncoordinated polyphosphide anions have been obtained by solution-based methods (Baudler, Polyphosphorus Compounds—New Results and Perspectives. Angew. Chem. Int. Ed. Engl. 1987 May; 26(5), 419-441; Baudler, et al., Trilithium Heptaphosphide, Dilithium Hexadecaphosphide, and Trisodium Henicosaphosphide. Inorg. Synth. 1990, 27, 227; von Schnering, et al., Chemistry and structural chemistry of phosphides and polyphosphides. 28. Bis(tetraphenylphosphonium) hexadecaphosphide, a salt with the new polycyclic anion P162. Angew. Chem. Int. Ed. Engl. 1981, 20: 594; Miluykov, et al., Facile routes to sodium tetradecaphosphide Na4P14 and molecular structure of Na4(DME)7.5P14 and Na4(en)6P14 (DME=1,2-dimethoxyethane; en=ethylenediamine). Z. Anorg. Allg. Chem. 2006, 632(10-11): 1728-32), which can be explained by the difficulty in isolating these species. In general, the highly reactive polyphosphide fragments need to be captured with organic or organometallic reagents.
The long history of polyphosphides notwithstanding, there is currently a growing interest in the study of these species. Research efforts in polyphosphide chemistry have been fueled by aspirations to control the activation of the P4 molecule (Cossairt, et al., Early-transition-metal-mediated activation and transformation of white phosphorus. Chem. Rev. 2010 Jul. 14, 110(7), 4164-77; Cummins, Terminal, anionic carbide, nitride, and phosphide transition-metal complexes as synthetic entries to low-coordinate phosphorus derivatives. Angew. Chem. Int. Ed. Eng. 2006 Jan. 30, 45(6), 862-70), known as the white allotrope of the element (Pwhite), and by the recent discovery of phosphorene as a promising graphene analogue with a finite direct band gap (Reich, Phosphorene excites materials scientists. Nature. 2014 Feb. 6, 506(7486), 19; Xia, et al., Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics. Nat. Commun. 2014 Jul. 21; 5: 4458; Liu, et al., Phosphorene: an unexplored 2D semiconductor with a high hole mobility. ACS Nano. 2014 Apr. 22, 8(4), 4033-4041; Li, et al., Black phosphorus field-effect transistors. Nat. Nanotechnol. 2014 May, 9(5), 372-377; Liu, et al., The effect of dielectric capping on few-layer phosphorene transistors: tuning the Schottky barrier heights IEEE Electron. Device Lett. 2014 May, 35(7), 795-797).
Most polyphosphides prepared by solid-state methods are insoluble in common organic solvents and exhibit very high chemical stability (von Schnering & Mille, Chemistry and structural chemistry of phosphides and polyphosphides. 48. Bridging chasms with polyphosphides. Chem. Rev., 1988 January; 88 (1): 243-273; Bawoh & Nilges, Phosphorus Rich d10 Ion Polyphosphides and Selected Materials. Z. Anorg. Allg. Chem. 2015, 641(2), 304-310) In contrast, the solution methods furnish soluble and reactive polyphosphide fragments, many of which were not detected in the solid-state reactions. Therefore, the need for a broader exploration of solution-based routes cannot be overstated, as these synthetic methods provide access to different polyphosphide species as a result of kinetically controlled, rather than thermodynamically controlled, reaction pathways. Not only do these species exhibit fascinating reactivity (Turbervill & Goicoechea, From clusters to unorthodox pnictogen sources: solution-phase reactivity of [E7]3− (E=P—Sb) anions. Chem. Rev. 2014 Nov. 12, 114(21), 10807-10828) but they also might serve as precursors for high-performance materials, including 2D semiconductors (Reich, Phosphorene excites materials scientists. Nature. 2014 Feb. 6, 506(7486), 19; Xia, et al., Rediscovering black phosphorus as an anisotropic layered material for optoelectronics and electronics. Nat. Commun. 2014 Jul. 21; 5: 4458; Liu, et al., Phosphorene: an unexplored 2D semiconductor with a high hole mobility. ACS Nano. 2014 Apr. 22, 8(4), 4033-4041; Li, et al., Black phosphorus field-effect transistors. Nat. Nanotechnol. 2014 May, 9(5), 372-377; Liu, et al., The effect of dielectric capping on few-layer phosphorene transistors: tuning the Schottky barrier heights IEEE Electron. Device Lett. 2014 May, 35(7), 795-797) and lithium-ion battery anodes (Wang, et al., Nano-Structured Phosphorus Composite as High-Capacity Anode Materials for Lithium Batteries. Angew. Chem. Int. Ed. 2012 September; 51(36):9034-9037).
The majority of solution-based routes for producing polyphosphides employ the toxic and flammable Pwhite allotrope, strongly reducing conditions, and/or cryogenic solvents (Baudler, Polyphosphorus Compounds—New Results and Perspectives. Angew. Chem. Int. Ed. Engl. 1987 May; 26(5), 419-441; Baudler, et al., Trilithium Heptaphosphide, Dilithium Hexadecaphosphide, and Trisodium Henicosaphosphide. Inorg. Synth. 1990, 27, 227; von Schnering, et al., Chemistry and structural chemistry of phosphides and polyphosphides. 28. Bis(tetraphenylphosphonium) hexadecaphosphide, a salt with the new polycyclic anion P162. Angew. Chem. Int. Ed. Engl. 1981, 20: 594; Miluykov, et al., Facile routes to sodium tetradecaphosphide Na4P14 and molecular structure of Na4(DME)7.5P14 and Na4(en)6P14 (DME=1,2-dimethoxyethane; en=ethylenediamine). Z. Anorg. Allg. Chem. 2006, 632(10-11): 1728-32). Such methods, therefore, are difficult to scale up, which limits the potential uses of polyphosphides and hinders more extensive studies of their reactivity. There have been a few reports whereby Pred was used to prepare species such as K3P7, but the solvents were limited to liquid ammonia or ethylenediamine in combination with strongly reducing agents (Na or Na—K alloy) (Miluykov, et al., Facile routes to sodium tetradecaphosphide Na4P14 and molecular structure of Na4(DME)7.5P14 and Na4(en)6P14 (DME=1,2-dimethoxyethane; en=ethylenediamine). Z. Anorg. Allg. Chem. 2006, 632(10-11): 1728-32; Schmidbaur & Bauer, An improved preparation of tris(trimethylsilyl)heptaphosphine. Phosphorus Sulfur Silicon Relat. Elem. 1995, 102(1-4), 217-219).
As such, there is a deficiency in the art to produce soluble polyphosphides from red phosphorous. As noted above, the difficulties in the art with respect to solubilizing Pred, along with the highly toxic materials used to solubilize Pred, evidence an unmet need in the art for methods of dissolving or solubilizing Pred or polyphosphides thereof in a liquid medium.